Conventionally, in order to prevent thefts in large volume retailers and the like, magnetic sensors are used. The element of such a magnetic sensor is formed with a warning thread that is formed of an amorphous ferromagnetic alloy and a magnetic bias thread that is formed of a semi-hard magnetic material.
As the semi-hard magnetic material for the magnetic bias thread, for example, a semi-hard magnetic material is proposed that is formed with 8.0 to 25.0 mass percent of Ni, 0.5 to 3 mass percent of Ti, 1.5 to 4.5 mass percent of Al and the remainder of Fe (see, for example, patent document 1). It is disclosed that this semi-hard magnetic material has a coercivity Hc of 1000 to 2400 A/m and a residual magnetic flux density Br of 1.3 T or more, and in particular, as an advantageous alloy, a semi-hard magnetic material containing 13.0 to 17.0 percent of Ni, 1.8 to 2.8 percent of Al and 0.5 to 1.5 percent of Ti is disclosed, and in its embodiment, semi-hard magnetic materials each containing high percentages of Ni, that is, a 15.0 percent of Ni and a 18.0% of Ni are disclosed.